It has been reported in recent years that a ligand of GPR40, which is one of the G Protein-Coupled Receptors (GPCR), is fatty acid and GPR40 in pancreatic β cell is deeply involved in insulin secretion action (see Nature, 2003, vol. 422, pages 173-176). Thus, a GPR40 agonist promotes insulin secretion, a GPR40 antagonist inhibits insulin secretion, and the agonist and the antagonist are useful as a therapeutic agent for type 2 diabetes, obesity, impaired glucose tolerance, insulin resistance, neurodegenerative diseases (e.g., Alzheimer's disease) and the like (see WO02/057783).
There are many compounds reported to be useful as therapeutic agents for diabetes.
For example, WO03/066574 discloses that aromatic amino acid derivatives represented by the formula:
    [X: halogen atom etc.; Y: O etc.; i: 1 etc.; m: 0, 1, 2; n: 1 etc.; R1: H etc.; R2: H etc.; R3: phenyl group substituted by pyridyl etc., and the like]    are expected to have an action to suppress hyperglycemia.
WO02/053547 discloses that a compound represented by the formula:
    [R1: optionally substituted 5-membered aromatic heterocyclic group; X: bond etc.; Q: C1-20 divalent hydrocarbon group; Y: bond etc.; ring A: optionally substituted aromatic ring; Z: —(CH2)n-Z1-(n=1-8, Z1=O etc.); ring B: optionally substituted pyridine, benzene etc.; U: bond etc.; W: C1-20 divalent hydrocarbon group; R3:—OR8 (R8═H etc.) etc.] is useful as an agent for the prophylaxis or treatment of diabetes, hyperlipidemia, impaired glucose tolerance and the like.
However, it has not been disclosed at all that these known therapeutic drugs for diabetes have a GPR40 receptor function modulating action, and additionally there is no report on a compound having a GPR40 receptor function modulating action (compound useful as a GPR40 agonist or GPR40 antagonist). Under the circumstances, development of a compound having a GPR40 receptor function modulating action has been desired.